MgTiO3Hx and CaTiO3Hx perovskite compounds for hydrogen storage applications

Abstract

The first principle calculations are used to investigate hydrogen storage properties of MgTiO3Hx and CaTiO3Hx (x = 0, 3, 6, and 8) perovskite compounds in cubic phase (Pm3 m). In order to examine the stability of these compounds, formation enthalpies are calculated and all compounds (except MgTiO3H6 and MgTiO3H8) are found to be stable. The second order elastic constants and related polycrystalline elastic moduli (e.g., shear modulus, Young's modulus, Poisson's ratio, Debye temperature, sound velocities) are determined and the results are discussed in detail. The mechanical stability determination indicates that MgTiO3, CaTiO3, and CaTiO3H6 compounds are only stable compounds and also MgTiO3 and CaTiO3H6 are ductile while CaTiO3 is a brittle material. Also, the mechanical anisotropy is discussed via two-dimensional (2D) and three-dimensional (3D) surfaces for mechanical stable compounds and they are found to have anisotropic behaviour (except linear compressibility for MgTiO3, CaTiO3). Electronic band structure and corresponding partial density of states (PDOS) and charge density have been plotted. Bader charge analysis have been done. MgTiO3 has metallic behaviour whereas CaTiO3 and CaTiO3H6 have semiconductor behaviour. Among all compounds, CaTiO3H6 is found to be only one that could be used in the hydrogen storage applications. For this compound, the gravimetric hydrogen storage capacity is calculated as 4.27 wt% and the hydrogen desorption temperature is obtained as 827.1 K. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.